Patent GB-629295-A (GB)
Title: Improved automatic control system for ship propulsion
IPC: H02P9/02
Filed: 1946-11-22
Abstract: 629,295. Automatic speed-control systems. BRITISH THOMSON-HOUSTON CO., Ltd., JEWITT, D. E., BARWICK, E. C., ADKINS, B., and BOURNE, S. N. Nov. 22, 1946, No. 34712. [Class 38 (iv)] [Also in Group XXXVIII] An automatic speed-control system for prime movers for ship propulsion, in which the fuel supply is controlled by selsyn receivers coupled to a master selsyn transmitter, the setting of which is normally determined by comparing the output of a tachometer generator with a pre-set voltage, includes also an over-riding power limit control arranged so that whenever the selsyn transmitter is in a position beyond that corresponding to the setting of the power limit control, the selsyn transmitter is moved in a direction to reduce the fuel supply to restore correspondence. A voltage proportional to the setting of the speed-control lever 22, Fig. 1, is tapped off potentiometer 23 and applied to a polarized relay 29 in opposition to the output of a tachometer generator 25 coupled to the combined output of the prime movers. Any unbalance between these voltages closes contacts 30, 31 or 30, 32 which (subject to the power limit control) energize contactors 33 or 34 in the armature circuit of a reversible pilot motor 18 which drives the rotor of the master selsyn transmitter 11 to cause the selsyn receivers 10 to open or close the fuel admission valves. The over-riding power limit lever 21 carries a contact 42, which when the lever is rotated in a clockwise direction, completes the circuit of contactor 33 through a contact 43 mounted on a rotatable disc 20, enabling the system to operate as above described. When the lever 21 is in the maximum power position shown, the circuit of contactor 33 is broken and only speed reduction can be effected. When the lever is moved anticlockwise, contacts 39, 40 short-circuit relay contacts 30, 32 causing speed reduction until the follow-up disc 20, which is coupled to selsyn 11, is rotated sufficiently to open contacts 39, 40. In a modification, Fig. 2 (not shown), the polarized relay and contactors are replaced by an amplidyne generator having fields energized in opposition by the speed governing potentiometer and the tachometer generator, the output current being applied to the pilot motor. A rectifier in the quadrature circuit of the amplidyne allows the build-up of a voltage of such polarity as to effect only a speed-reducing movement of the pilot motor, unless the power limit lever is in a position short-circuiting the rectifier and allowing normal operation. To reduce power, the circuit between the potentiometer and the amplidyne field is opened. In a further modification, Fig. 4, the resultant voltage of the opposed potentiometer 23 and generator 25 is applied to the field 51a of amplidyne 50, the output of which is used as before. Power limitation is effected by a rectifier 57a which allows the field 51a to be excited only in such sense as to reduce speed, unless the rectifier is short-circuited by contacts 2x, 2y. To reduce power, contacts 2x, 2z excite the amplidyne field to reduce speed. An auxiliary field 11b in series with the output and with a rectifier bridge 13a having a bias potential from potentiometer 14a across the other diagonal prevents the output voltage from rising above the bias voltage. A further auxiliary field 11c energized from a transformer 15a which has its primary across the generator 25 prevents hunting. In a further modification, Fig. 3 (not shown), the resultant of the opposed voltages from the potentiometer and the tachometer generator is applied directly to the armature of the pilot motor, a rectifier is inserted in the circuit to prevent operation in the speed increase direction when maximum power has been reached, and the armature is directly energized from the supply mains to reduce speed if the maximum power is exceeded. This power-control is effected by two-cam operated contacts, the cam being manually slidable along a splined shaft by the power-control lever, and movable on a screwthread by rotation of the selsyn transmitter. The tachometer generator may have a series field winding to increase the control effect. Specification 542,248 is referred to. The Provisional Specification states that an electronic discharge amplifier may be used instead of the amplidyne generator.